Catalytic converters are typically assembled by stuffing a substrate assembly into a converter outer shell. The substrate assembly is formed by wrapping an insulating mat around a catalytic substrate. The mat is then held in place by tape. Pressure is applied to the substrate assembly to compress the mat around the catalytic substrate. An outer diameter of the substrate assembly is measured during application of the pressure. A predicted outer diameter of the converter outer shell is then determined based on this outer diameter measurement of the substrate assembly. The substrate assembly is then lightly stuffed into the converter outer shell and the converter outer shell is subjected to subsequent forming operations to reduce the converter outer shell to the predicted outer diameter.
This traditional assembly method has some disadvantages. The subsequent forming operations utilize a complex eight (8) segmented tool assembly, which is time consuming and expensive. Further, each final assembled catalytic converter should have a desired density characteristic. No density predictions, measurements, or calculations are performed during this traditional assembly method. Thus, there is no way to determine during assembly whether a final assembled catalytic converter has the desired density characteristic.
Another assembly method utilizes a hard stuff approach. In this approach, the insulating mat is wrapped around the catalytic substrate in a manner similar to that described above. No diameter measurements are taken of the substrate assembly. The substrate assembly is simply hard stuffed into a converter outer shell that has a fixed final diameter.
In this assembly method, the amount of push-in force is measured to indirectly determine whether or not the catalytic converter will have the desired density characteristic. If the push-in force is too low then the catalytic converter is not acceptable and is scrapped. This process is costly as the converter outer shell, mat, and catalytic substrate are all scrapped when the push-in force is too low.
Another hard stuff assembly process weighs the insulating mat prior to hard stuffing. If the weight of the insulating mat is too low, then the insulating mat is scrapped. While this identifies a problem prior to stuffing the substrate assembly into the converter outer shell, this method still has the disadvantage of a high scrap rate.
Thus, there is a need for a method of assembling a catalytic converter that reduces scrap rates, and which does not require additional forming steps on the converter outer shell subsequent to stuffing. The method of assembly should be simple, efficient, and more cost effective than prior methods in addition to overcoming other deficiencies in the prior art outlined above.